Tuned 395xp - ignition timing

[bmp01]

Nope,  I'm screwed as soon as the flywheel is off as well. All my numbers will be wrong by the amount I move the flywheel on the crank. It wasn't very clever really,  I wasn't thinking more than the one step when I did it, just wanted to know the existing timing. 

Piston stop, yep, much better than my approach, doesn't move about.  Just so long as  you're a decent distance away from TDC. Making a bespoke one is on my todo list for tomorrow.

What do you kniw about strobes ? Must be some timing circuit inside them?  Can't believe they flash as soon as the sensor detects the spark. ... nothing can be that quick,  surely?

 

Edited January 12, 2020 by bmp01

[wyk]

Depending on a few factors, an electrical impulse/wave travels about 70% the speed of light in copper, with currents traveling around 1/100th the speed of light(c=nearly 300,000km/second in a void) through a metal wire. Assuming direct current, the signal reaches the bulb so fast it's almost as though there is no delay(unless you are a subatomic particle or a photon).

The timing light likely has some sort of inductive set up with wires coiled around or terminate at a bulb, causing it to flash when there is an electric signal. Unless it's a rather fancy strobe, it's likely all wiring.

 

[spudulike]

So, going back to my bespoke patented method, using another machine, put a flexible spacer stop in through the spark plug hole, push it against the cylinder wall and turn the flywheel clockwise until the spacer is holding the piston off TDC and photograph the flywheel. All you then need to do on your machine is to put a smear of Loctite around the crank taper, slide on your flywheel, using the same spacer on your machine, replace the flywheel giving another 5 degrees of advance and tighten the nut carefully and keep rechecking the position of the flywheel - it can be tapped round with a drift and hammer if necessary and once reasonably tight, use a stop and crank it up then check the position again.

This way you will get it right within a degree or two.

Any other method is a bit hit or miss.

[htb]

Steve would that be the same as base of barrel machined and base gasket thinner, so for a given thickness of spacer stop the crank would be in a slightly different position from modded to standard?. Correct me if I am wrong.

[peatff]

For the scooter I downloaded a timing disc picture from the internet and printed it to size then stuck it to the flywheel. I used an old spark plug with the middle knocked out and a 5mm bolt through the middle to make a piston stop, turn the flywheel one way then the other to mark TDC then turn the flywheel back to get the advance you want.I got it to 22° and checked it with the strobe and it seems to work.

[bmp01]

52 minutes ago, wyk said:

Depending on a few factors, an electrical impulse/wave travels about 70% the speed of light in copper, with currents traveling around 1/100th the speed of light(c=nearly 300,000km/second in a void) through a metal wire. Assuming direct current, the signal reaches the bulb so fast it's almost as though there is no delay(unless you are a subatomic particle or a photon).

The timing light likely has some sort of inductive set up with wires coiled around or terminate at a bulb, causing it to flash when there is an electric signal. Unless it's a rather fancy strobe, it's likely all wiring.

 

Ok, I want that to be the case (just wires, no electroncs). I like simples.

I was looking for an explanation for why the strobe timing and the tacho went beserk when the saw started misfiring. ... which I now think was fueling induced not coil induced. Understanding the tacho is easy - its looking at the time between sparks to determine engine speed, if engine speed is changing dramaticlly due to musfire then the tacho can't follow it sensibly.  But the strobe, if it flashes in response to a spark and the coil isn't limited type, then the spark and strobe should keep happening at the ssme point in the engine cycle. Maybe the strobe can't operate at high 2 stoke engine speeds, it's a plain and pretty old strobe I'm using.

I'll pull the covers off  it and hope to find just wires.

[bmp01]

9 minutes ago, htb said:

Steve would that be the same as base of barrel machined and base gasket thinner, so for a given thickness of spacer stop the crank would be in a slightly different position from modded to standard?. Correct me if I am wrong.

It would be different for an engine that has 20 thou squish compared to a saw that has 40 thou of squish. Squish being the distance from top of piston to underside of chamber at TDC. You'd have to know what the squish was in ech case and then move the piston down a further equal amount on both set ups. Halfway down the stroke the squish gets less signifcant but its still there in the detail. 

[spudulike]

28 minutes ago, htb said:

Steve would that be the same as base of barrel machined and base gasket thinner, so for a given thickness of spacer stop the crank would be in a slightly different position from modded to standard?. Correct me if I am wrong.

It would change it but it is still more accurate than pretty much any other method bar swapping the flywheel.

[htb]

8 minutes ago, spudulike said:

It would change it but it is still more accurate than pretty much any other method bar swapping the flywheel.

OK just thought I better ask.

[wyk]

15 hours ago, bmp01 said:

Ok, I want that to be the case (just wires, no electroncs). I like simples.

I was looking for an explanation for why the strobe timing and the tacho went beserk when the saw started misfiring. ... which I now think was fueling induced not coil induced. Understanding the tacho is easy - its looking at the time between sparks to determine engine speed, if engine speed is changing dramaticlly due to musfire then the tacho can't follow it sensibly.  But the strobe, if it flashes in response to a spark and the coil isn't limited type, then the spark and strobe should keep happening at the ssme point in the engine cycle. Maybe the strobe can't operate at high 2 stoke engine speeds, it's a plain and pretty old strobe I'm using.

I'll pull the covers off  it and hope to find just wires.

That may be due to a limited coil. Does it happen at high rpm?